Cocaethylene (the ethyl ester of benzoylecgonine) is a product of the interaction between ethanol and cocaine. The results of preclinical studies and of a pilot clinical study have shown cocaethylene to produce pharmacologic effects similar to those of cocaine. However, no information is available concerning the potency and pharmacokinetics of cocaethylene in comparison to those of cocaine in humans. We report the results of a single-blind, crossover study in which six male, healthy, paid volunteers, who were moderate users of cocaine, were intravenously injected with the water soluble fumarate salt of cocaethylene (0.25 mg/kg cocaethylene base) or an equivalent dose of the water soluble hydrochloride salt of cocaine (0.25 mg/kg cocaine base). Each dose was dissolved in normal saline and injected over a 1-min interval. Test sessions were separated by a 1-week interval. The variables measured were: cocaine and cocaethylene plasma concentrations, subjective and cardiovascular effects. The results indicate, that in comparison to cocaine, cocaethylene had a significant smaller elimination rate constant (0.42 versus 0.67 l/h), had a longer elimination half-life (1.68 versus 1.07 h), and induced ratings of "high" and changes in heart rate that were of lower magnitude (65%, and 43%, respectively). During the period of time that pharmacologic effects were present the plasma concentrations of cocaine and cocaethylene were statistically indistinguishable. This finding supports the conclusion that in humans cocaethylene is less potent than cocaine.